Heretofore, it has been well known to provide switches for overhead track systems along which trolleys are either manually or power driven and particularly for the movement of goods suspended from the track by the trolleys between stations for processing or for storing goods. For example, overhead conveyors having tracks and switches in the tracks are commonly used in warehouse operations and also in meat-processing plants. Exemplary of the type of mechanisms heretofore known are disclosed in U.S. Pat. Nos. 2,746,397, 3,818,836, and 4,646,646. These switches include a plurality of levers and links arranged between lifting track sections, the position of which control the movement of trolleys along intersecting tracks or rails. It is also known, as shown in these patents, to automatically allow the movement of a trolley through the switch in one direction without manually or otherwise adjusting the switch. Movement in the opposite direction is controlled by adjustment of the switch.
The heretofore known switches have included a shaft about which the track lift pieces are connected to the switch linkage pieces. This connection which directly rotates about the shaft has caused considerable problems including overtightening of the shaft prohibiting free rotation, loosening of the shaft causing misalignment of the lift piece with the track, and undertightening of the shaft also leading to misalignment of the lift piece with the track. Overall the shafts heretofore used in overhead track systems have needed considerable and costly maintenance, have been difficult to service in the field, and have caused considerable difficulties in system operation. For example, improper seating or alignment of a lift piece may cause trolley derailment, trolley and/or track damage, damage to goods carried by the trolleys, and sometimes injury to persons working underneath the track or rail.